The invention relates to metal carbene complexes. More particularly, it relates to catalyst systems comprising metal carbene complexes.
Catalysts previously known in the art are described in, for example, U.S. Pat. No. 5,312,940 to Grubbs et al. These catalysts include bis(phosphine) complexes which involve the use of costly phosphine (PR3) ligands. The stabilities of such systems, as determined by, for example, P—C bond degradation at elevated temperature, are limited. Also, the rates at which bis(phosphine) catalysts carry out particular reactions are limited. Thus, industrial applications involving large-scale syntheses are not as efficient as they could be.
Previously available catalytic systems are also limited in their ability to make highly substituted ring-closing metathesis (RCM) products. Thus, bis(phosphine) catalysts cannot reliably close dienes to make tri-substituted cyclic alkenes, and they fail to make tetrasubstituted cyclic alkenes in all but a few cases. Although Schrock catalysts are available to carry out this type of reaction, such systems are quite sensitive.
Thus there exists in the art a need for a generally air- and moisture-sensitive catalyst system able to carry out RCM reactions efficiently and reliably, and also without excessive thermal sensitivity.